How to scale properly HDRI image, to be used in ASC-CDL HDR render?
I'm quoting here "
Clamps are dangerous creatures." @troy_s
The problem was that I had value in the clamp direct and indirect under Render>Sampling, so what happened is that Cycles was clamping all values above 1, while I was trying to get the sun brighter with no luck!! Lesson learned the hard way.
But wait, this is only part of the issue, this solved the high value absence puzzle, but not the absence of gradation.
Long Answer short, this is how it was solved, no need to say that the following parameters are obviously not a magic number to go with for every HDRI, since every HDRimage, good and bad ones, has it's own unique values and light conditions:
1- HDRI map strength: 18, yes I know it's crazy, but we're dealing with High Dynamic Range, we need a bed big enough for all the values of the HDRI to fit in. Just like the story, this is the Mushroom that made Alice grow to her size.
2- Slope value in Color Balance node in the compositor: 0.18, yes even more crazy, this is the mushroom that made Alice small enough to fit in the display reference door, remember that the mushroom made Alice shrink, proportionally, it didn't chop her off to pieces.
3- Power value in Color Balance node: 1.8, convex f-curve to distribute the values from high to low in a way that gives enough space for gradation.And here's the result.No LookFake Colors Look 

Of course these values would work for this particular HDR image, not necessarily a rule, but as a rule of thumb, I guess I'll be using high value for HDR image, and crank it down using the slope value, and expand the curve using a power value higher than 1, in order to make a concave easing out curve.

Finally, I'm not a tech person, and I know my description above sounds funny, on the other hand, the values still need some tweaking because there are still some white spots, which refer to over exposed areas, but at least I'm very close to achieve a good result. If you check the answer in this link is way more descriptive of this case, and in much better way. Following the instructions in this link, 14.5 is more accurate range for a standard case, for a standard HDR image.  Furthermore, here are some experiments I did with other HDRimages: